I'll add another use case for letting an AI go ham: many small, atomic refactors where the name of the game is never breaking anything.

My personal OSS projects don't have the scale to necessarily make this worth it, but at work I run three pipelines using Barnum (https://barnum-circus.github.io/). First, one that ingests files, identifies refactors (from a pre-approved list), and places a precise description of the refactor to be done in a queue; second, one that reads from said queue, implements and creates PRs (there is a lot of "check that the PR is correct" here as well); and a third that babysits PRs until they land. I've landed hundreds of PRs in this way, with very little effort on my part.

I recently in $COMPANY had a coworker try fable to do a refactor where not breaking anything was the game.

It broke something at the first PR.

I think we’re not there yet.